Protecting the future of UK sheep farming

Anthelmintic resistance is the ability of worms to survive the normal dose of a wormer and pass that ability on to its offspring. This results in the proportion of resistant worms in the population increasing over time. Worms can be resistant to one class or several classes of wormer.

The percentage of resistant worms, and the number that survive treatment, increases with time as illustrated:

The impact of wormer resistance on the farm will not be immediately obvious. As resistance develops, there is a gradual increase in the number of worms surviving treatment. The worms left behind will hold the lambs back, decreasing growth rates by up to 50% before there are any visible signs that the wormer treatment has not been fully effective¹. The level of challenge, and therefore the need to treat for these worms during the summer and autumn, is weather dependent.

This is why we need to change current practices and adopt a more sustainable approach to worm control - even when there are no visible signs of decreased performance or lack of wormer efficacy.

Anthelmintic resistance is one of the biggest challenges to the health and profitability of sheep and affects the entire sheep industry: a recent study found that parasitic worms has been estimated to cost the European livestock industry more than €1.8 billion per year, with drug-resistance costing at least €38 million per year in production losses and treatment costs.^3,4

In the last 10 years the number of reports of resistance to the three older classes have been increasing. Research from Wales Against Anthelmintic Resistance Development (WAARD) showed the majority of farms surveyed had a degree of resistance to one or more of the three older wormer classes¹.

This not only means that overuse of the three older classes will continue to expedite the development of resistance, but also means that farmers are not seeing a true return on their investment in their flock.

Once anthelmintic resistance has developed, it is not reversible, so we need to do everything possible to slow the development of resistance.

Once anthelmintic resistance has developed, it is not reversible, so we need to do everything possible to slow the development of resistance.

The speed at which resistance develops depends on how carefully and sustainably anthelmintics are used. This means avoiding practices that drive resistance development, such as:

It's always best to check how effective a treatment has been by doing a post-treatment drench check, with a faecal egg count, after every treatment. 

Use Zolvix™ as a 'break dose' in lambs in the mid-late season as a break dose in lambs (any time from July onwards depending on worm burden; individual farm needs will vary). By the latter part of the grazing season, most lambs will have received wormer treatments involving one or more of the group 1, 2 or 3 products. Any worms resistant to these groups will have survived these treatments and, because they can live inside a sheep for months, they accumulate over the season. This population of worms in the lambs is therefore made up of a higher proportion of anthelmintic resistant worms than the population in refugia when the levels of resistance are low.

Treatment with an effective product, such as Zolvix, will remove these worms and stop them from reproducing and adding their genes to the overall population. To get the best result, Zolvix should be incorporated into a worm control programme when the level of resistant worms is low².

Gregor explains how incorporating Zolvix™ into his worm control strategy has managed worm burdens so effectively that his lambs achieve the target growth rates:

“Executing an effective worming programme is vital for us, as it allows us to protect investment already made in our flock, while protecting stock due to be sold the following year. To clear worm burdens around September time, we’ve opted to use an annual late season break dose using Zolvix as part of our worming protocol. It gives us the result that we need to get – which is getting stock thriving and growing again.”

Use Zolvix™ as a farm protection quarantine dose for any stock moving on to the farm. All sheep coming on to the farm are a risk and should be yarded and treated on arrival. This includes both incoming stock and stock coming back on to the farm from a different holding. 

There are five elements to quarantine treatments:

When a treatment is needed for fluke at the same time as worms, a combination product can be used such as

Neil explains the benefits he's found by using Zolvix in his worming strategy for both a quarantine dose and a mid-late season break dose:

“Having an effective worming programme helps us ensure our lambs continue to grow and meet their target weights, as quickly and efficiently as possible. We’re doing all we can to slow down resistance to all wormer groups, by only drenching when required, breaking the resistance cycle by adding Zolvix into our strategy, and undertaking post-drench efficacy tests to monitor wormer performance. By using Zolvix, our lambs are hitting their target weights quicker and spending less time on-farm, due to them gaining weight more efficiently, making our production costs lower.”

A farmer survey⁵ showed that 86% of farmers thought their wormers were working as well as they always had. The same survey showed that the majority of farmers judged this on “the look and condition of the sheep”.

However, data shows that lamb performance/growth rate will be reduced by up to 50%² by a worm burden (e.g. resistant worms left behind after treatment), with no visible sign that the lambs are unhealthy.

Worm resistance is an invisible problem, only becoming visible when it's too late.

However, farmers incorporating Zolvix™ in their worm control strategy have found its efficacy at managing worm burdens means their lambs achieve the target growth rates: